CS457 - System Performance Evaluation - Winter 2008
Questions and Comments
- Due time for A2.
Lecture 17 - Simulation
Models
Based on a model, which is an abstraction of the system.
- queueing models
- requests arrive
- wait
- get service
- depart
- one queue models
- multiple queue models
- queueing networks
Types of models
- stochastic models
- define state
- continuous time models
- discrete state models
Model development
- You did this before
- Understand the system
- What is the goal?
- Determine the components
- e.g., server, job
- sometimes called `entities'
- have attributes, e.g.
- server: capacity
- job: service required
- system (client?): interarrival time
- Cheat and steal
- Select the type of queueing model
- single server queue,
- single service facility with multiple servers,
- network of queues
- Specify attributes that need algorithms
- e.g., scheduling disciplines for resources
- Specify workload parameters and performance metrics
- remember (guess what?) the goal
Example. Routing for automated telephone support
- single server, two classes of request
- queueing models have a scheduling algorithm, such as
- FCFS
- priority-based FCFS
- round robin, aka take turns
- each has a natural structure
- FCFS: single queue
- priority-based: multiple queues
- round-robin: multiple queues
- with multiple classes
- arrival rate adds: r = r1 + r2
- interarrival time adds reciprocals: t = 1/r = 1/(r1 + r2 ) =
1/(1/t1 + 1/t2) = t1*t2 / (t1 + t2)
or 1/t = 1/t1 + 1/t2
- Parameters
- interarrival time: per class
- length of transaction: per class
- service capacity: per class
- queueing algorithm
- Performance metrics
- waiting time: per class
This is used to determine the cycle time of the advertising you
listen to. Just joking!
- utilization
No point in hiring any more support staff than you need.
For a more CS-like example see this pdf.
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